Breathable multifoil in walls? What type?

[paulc]

This is a really helpful little sum up thanks!! Would you apply the same rules to pitched roof insulation?
And do you have a link to the historic environment Scotland research? Would be interesting to have a read.

The link is in the post you quoted. HES has a bunch of other articles on old buildings, so it is worth browsing their site.

 

[Cherryburn]

I think people misunderstand multifoils somewhat. It's not really intended to be used in isolation. However, if it's used in place of other products somewhere there would already be an air gap then it can help to reduce the amount of other insulation you might need without increasing the thickness of the system. For example a pitched roofing membrane, or vapour barrier on a flat roof or modern timber framed construction.